Solenoid Coils for Contactors / Relays typically begin making obnoxious 120 Hz humming noise due to:
[*]Contaminates between core laminations,
[*]Loose core laminations,
[*]Mis-Alignment of Solenoid,
[*]Contacts not seating completely (aka "chatter").
As mentioned, if the laminated core of the Contactor's Solenoid Coil has dirt build up or rust between laminations, this will cause humming (120 Hz humming to be precise).
This could occur on the stationary part, the moving / sliding part, or both.
If the laminations become loosened, this also will cause noisy operation.
This also could occur on the stationary part, the moving / sliding part, or both.
If the contacting "face" points of the core sections do not line up evenly, have excessive build-up on them, are slightly twisted off axis, or if one (or both) side(s) doesn't "pull-up" completely- resulting in a slight gap between stationary and moving cores when the Contactor is locked in, this will cause noise and heat.
If the sliding portion of the Contactor does not completely lock-in, this will cause excessive noise and heat.
If you have the time (and patients
) to clean it, try that.
Need to remove the cores from around the coil and from the sliding assembly.
Clean cores with appropriate solution, let dry completely (maybe even dry in an oven at the lowest setting!), then re-assemble.
On a mis-aligned contactor, try loosening up the mounting screws during operation to see if this causes a drammatic reduction in noise. If so, re-mount contactor as needed.
Be sure to include isolation materials between contactor and enclosure!
For extremely mis-aligned contactors (out of alignment due to someone / something hitting it really hard, or installing it across an uneven surface), or contactors with a seating problem, there may be only one thing to do - replace the entire contactor!
Also, for severly rusted / loosened laminations, might need to replace core(s), contact assembly or complete contactor!